Transmural (involvement of more than the inner one-half of the myocardial wall) left ventricular necrosis or fibrosis is most often secondary to severe (more than 75% cross-sectional area) narrowing by atherosclerotic plaques of 1 or more of the major epicardial coronary arteries. Myocardial infarction also may occur without significant narrowing of an epicardial coronary artery in several conditions, including hypertrophic cardiomyopathy, dilated cardiomyopathy, left or right ventiruclar outflow obstruction, and anomalies of coronary arterial origin or course. Another condition associated with myocardial infarction without significant narrowing of 1 or more of the epicardial coronary arteries is cardiac amyloidosis. Of 61 necrospy patients aged 21 to 97 years (mean 64) with cardiac amyloidosis severe enough to cause cardiac dysfunction studied in this laboratory during the past 28 years, 3 (5%) had transmural necrosis and 5 (8%) had transmural fibrosis of the left ventricular wall, and 53 (87%) had neither necrosis nor fibrosis. One patient with necrosis, 3 with fibrosis, and 9 with neither necrosis nor fibrosis and 1 or more epicardial coronary arteries severely narrowed by atherosclerotic plaque. Two patients with necrosis and 2 with fibrosis, plus 44 with neither, had no epicardial coronary artery narrowed more than 75% in cross- sectional area by atherosclerotic plaque.